This invention relates to backscatter thickness measuring instruments and particularly to a device for measuring the thickness of a coating on a strip of substrate material moving from a feed supply to a take-up location at a predetermined speed.
Backscatter instruments are used to measure thickness of coatings by irradiating a coating on a substrate and counting the particles backscattered therefrom. To make a measurement the user must position the probe, having both source of radiation for irradiating the coating and apparatus for detecting the particles backscattered from the coatings, adjacent to the portion of the coating which is to be measured.
A backscatter measurement instrument is connected to the probe for counting the backscattered particles for a preselected time period and giving an indication of the coating thickness corresponding to this count. It is desirable that the probe and the portion of the coated material to be measured remain stationary with respect to one another during this measurement period. The longer this period of measurement the more accurate the result.
In the electronic industry manufacturers of coated substrates have developed efficient and economical processes for coating strips of substrate material. This is a highly developed art where coatings can be applied in the range of 30-100 micro inches with a high degree of uniformity. It has been determined that coating strips of substrate material is much more economical than coating substrates on a piece basis.
In recent years, there has been a particular need for an instrument for accurately measuring thickness of coatings on substrate materials, because gold is used for contact points in electronic circuits, and the price of gold has risen considerably. Accordingly, there has been an increased demand for accurate instruments to determine how much gold is being deposited in the coating process.
The process of coating strips of substrate material is a continuous one where the substrate material moves at a predetermined speed through the coating stage. Since the probe is preferably stationary with respect to the coated strip of substrate material during the backscatter thickness measurement period, it is necessary, with conventional instruments, to stop the coating process while the measurement is being made and then start it up again. This discontinuous stop and start process is quite time consuming and there has been a need for a device which could measure the coating thickness without having to stop the movement of the strip of substrate material.